Method and system for automatically detecting and controlling furnace operating condition of arc-furnace at charge melting stage

ABSTRACT

A SYSTEM FOR AUTOMATICALLY DETECTING AND CONTROLLING THE FURNACE OPERATING CONDITION OF AN ARC-FURNACE AT THE CHARGE MELTING STAGE IN WHICH SAID MELTING STAGE IS FURTHER DIVIDED INTO THE FIRST PERIOD, BORING DOWN PERIOD, ESTABLISHING PERIOD OF A SMELL POOL OF LIQUID, SHIELDED ARC PERIOD, AND FLAT BATH PERIOD, THE FIRST PERIOD, BORING DOWN PERIOD AND ESTABLISHING PERIOD OF A SMALL POOL OF LIQUID ARE RESPECTIVELY DETECTED BY FIRST DETECTING MEANS BASED UPON ELECTRODE POSITION AND LOWERMOST ELECTRODE POSITION INDICATING SIGNALS, AND THE SHIELDED ARC AND FLAT BATH PERIODS ARE DETECTED RESPECTIVELY BY THE POWER CONSUMPTION AFTER THE START SIGNAL OF ESTABLISHING PERIOD OF A SMALL POOL OF LIQUID HAS BEEN DERIVED AND BY DETECTING MEANS TO BE ENERGIZED BY SAID SIGNALS AND THE SIGNAL REPRESENTING THE ARC IMPEDANCE.   D R A W I N G

United States Patent Inventor Appl. No. Filed Patented Assignee Priority Morihiko Kawabe Yokohama-shi, Japan 883,003

Dec. 8, 1969 June 28,1971

Ishikawajima-Harima Jukogyo Kabushiki Kaisha Tokyo-to, Japan Feb. 20, 1969 Japan METHOD AND SYSTEM FOR AUTOMATICALLY DETECTING AND CONTROLLING FURNACE OPERATING CONDITION OF ARC-FURNACE AT [56] References Cited UNITED STATES PATENTS 3,431,344 3/1969 Borrebachi M 13/12 3,435,121 3/1969 Jackson 13/13 Primary Examiner-Bernard A. Gilheany Assistant ExaminerRoy N. Envall, Jr. Attorney-Nolte and Nolte ABSTRACT: A system for automatically detecting and controlling the furnace operating condition of an arc-furnace at the charge melting stage in which said melting stage is further divided into the first period, boring down period, establishing period of a small pool of liquid, shielded arc period and flat bath period; the first period, boring down period and establishing period of a small pool of liquid are respectively detected by first detecting means based upon electrode position and lowermost electrode position indicating signals; and the shielded arc and flat bath periods are detected respectively by the power consumption after the start signal of establishing period of a small pool of liquid has been derived and by detecting means to be energized by said signals and the signal representing the arc impedance.

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MOP////( 0 154144435 INVENTOR AI TORNEY METHOD AND SYSTEM FOR AUTOMATICALLY DETECTING AND CONTROLLING FURNACE OPERATING CONDITION OF ARC-FURNACE AT CHARGE MELTING STAGE DETAILED EXPLANATION OF THE INVENTION The present invention relates to a method and system for automatically detecting and controlling the furnace operating condition of an arc-furnace at the charge melting stage.

In the conventional system for regulating the power to be supplied to an arc-furnace at the melting stage, the programmed power supply method is used so that the power may be supplied to the arc-furnace independently of the furnace operating condition or the skilled labor regulates the power supply based upon his experience.

In the programmed power supply method, the electric power is regulated independently of the operating condition when the arc-furnace is once ignited so that the required power cannot be supplied at the desired .time and it does harm to the floor and lining of arc-furnace more first. In the latter method in which the skilled labor regulates the power supply, it is very difficult to detect the actual operating condition of the arc-furnace. Both of the above-described methods have the defects in the fact that the power is uneconomically consumed and that:the service lives of the arc-furnace itself and the electrical circuit are short.

In order to eliminate such defects as-described above the present invention provides a method and system for automatically detecting and controlling the furnace operating condition of an arc-furnace. at the. charge melting stage characterized by deriving the signals representing the position and the lowermost position of an electrode respectively; transmitting said signal representing the lowermost position of the electrode to detecting means for detecting thefirst period, boring down period and establishing period of a small pool of liquid respectively, detecting the shielded arc period by means of the power consumed after said establishing period of a small pool of liquid starting signal has been derived; and detecting the flat bath period by detecting means which is energized by said signals representing the position and the lowermost position of the electrode and the signal representing the arc impedance.

The above andother objects, features and advantages of the present invention willbecome more apparent from the follow-- ing description of one illustrative embodiment of the present invention with reference to the accompanying drawing.

. FIG. 1 is for explanation of the arrangement of a signal deriving member or signalgenerator for generating the signals indicating the lowermost position of an electrode and of the position of this electrode of an automatic detection and control system for detecting and controlling the arc-furnace operating condition when the charges are started to be melted in accordance with the present invention;

FIGS. 2 and 3 are graphs for explaining the relation between the time and the position of the electrode and the lowermost position thereof when the charges are started to be melted;

FIG. 4 is a block diagram of an electrical equipment of the system of the present invention; and

FIGS. 5 and 6 are graphs of IOO-ton and SO-ton arc-furnaces illustrating the number of times per unit time of the arc impedances exceeding the predetermined levels based upon the experiments.

Referring to FIG. I, the electrode driving, its position and its lowermost position detection device of the present invention comprises an arc-furnace I, an electrode 2 vertically placed in the furnace I, a sheave 3' fixed to a support 2' for the electrode 2, a drum 3 for winding therearound through the sheave 3' a length of rope 8 one end of which is fixedly secured to the support 2, a synchronous transmitter 4 and a synchronous receiver 5 which rotate in synchronism with the rotation of the drum 3, a potentiometer. 6 directly coupled to the synchronous receiver 5 and another potentiometer 7 driven through a cam 10 by the rotation of the synchronous receiver 5, whereby the electrode 2 may be driven upwardly and downwardly with respect to the arc-furnace I through the sheave 3' and the rope 8 by the rotation of the drum 3.

The forward or reverse rotation of the drum 3 has a predetermined functional relationship with the upward or downward movement of the electrode 2 with respect to the arc-furnace 1, that is the position of the electrode 2. Furthermore, the rotation of the drum 3 has a predetermined relationship with both of the synchronous transmitter 4 and receiver 5 and consequently with both of the potentiometers 6 and 7. Therefore, the potentiometer 6 generates the signal (a) representing the position of the electrode 2 whereas the potentiometer 7, the signal (b) representing the lowermost position of the electrode 2.

The electrical system of the automatic detection and control system of the present invention comprises, as shown in FIG. 4, a first group including a memory ME, a comparator C0,, a sampling device GR, a comparator CO all of which are coupled in parallel with a lead wire for transmitting the signal (b), a comparator CO coupled in series with the sampling device GR, a logic circuit AND, coupled to both of the comparators CO and CO and a comparator CO coupled to both of the lead wires for transmitting the signals (a) and (b) respectively and to a logic circuit AND and a second group including an arc impedance circuit A1,, for deriving the signals kZA which are a function of the arc voltage AE and the arc current Al, a third group for transmitting the signals kZA to the logic circuit AND through low pass filter LP, a rectifier RE, a comparator CO a pulse counter PC and a comparator C0 and a fourth group including an integrating wattmeter for integrating the power P consumed by the arc and a comparator C0 coupled tothe wattmeter.

In the automatic detection and control system of the present invention having the above-described arrangement, the relation between the position of the electrode 2 with respect to the arc-furnace l and time is illustrated in FIG. 2 while the relation between the lowermost position of the electrode 2 and time is illustrated in FIG. 3; As will be seen from FIG. 2, the position of the electrode 2 can be automatically controlled according to the five arc-furnace operating conditions, that is the first period A, the boring down period B, the establishing period of a small pool of liquid C,- the shielded arc period D and the flat bath period E.

For this purpose, the signal (b) representing the lowermost position of the electrode is stored in the memory ME at the ignition stage A where the current starts to flow through the electrode 2, the memory ME deriving the first period-start instruction (0).

Next the output signal from the memory ME is compared in the comparator C0, with the signal (b) representing the lowermost position of the electrode and when the difference between said two signals reaches a predetermined bias (voltage) 8,, the comparator C0,-is energized thereby deriving the boring down period-start instruction (d). Simultaneously, the signals (b) are stored per-unit time in the sampling device GR and the differences among the signals (b) at a predetermined time interval are transmitted to the comparator CO so as to compare these difierences with a predetermined bias (voltage) 8,. When the difference isless than the bias (voltage) B the output signal is derived from the comparator'CO,. Furthermore, when the signal'(b) is lessthan a predetermined bias (voltage) B the comparator CO operates, thus deriving the output signal, which is transmitted to the logic circuit AND, together with the signal from the comparator C0,. In the circuit AND,, establishing period of a small pool of liquid-start" instruction (e) for starting the establishing period of a small pool of liquid C is derived based upon said two signals.

The power P consumed after the instruction (e) has been derived is integrated by the integrating wattmeter lPC and when the consumed watt-hour reaches a predetermined bias 8-,, the comparator CO generates the "shielded arc period period-start" instruction (l). I

in the detection circuit group, after the shielded arc period-start"- instruction has been generated, the voltage signal kZA representing the arc impedance ZA is transmitted to low pass filter LF, then rectified by the rectifier RF and transmitted to the comparator C The number of times of the signals kZA exceeding a predetermined bias (voltage) B, is represented by pulses in .the comparator CO and transmitted to the pulse counter PC. The pulse counter PC counts the number of pulses per unit time and when the number of times in which the counted pulses are less than a predetermined number B, reaches a predetermined number, the comparator CO, generates the signal to be transmitted to the logic circuit AND a In the comparator C0,, the signal representing the position of the electrode 2 is compared with that representing the lowermost position of the electrode. When the difference therebetween exceeds a predetermined value 8., the output signal is transmitted to the logic circuit AND The circuit AND derives the fiat bath period-start" instruction (3) based upon the output signals from the comparators CO. and C0,.

After the instruction (3) has been derived, the tap voltage is reduced in a suitable manner so as to melt down.

FIGS. 5 and 6 illustrate the relation between the time and the number of times when the arc impedance signals exceeded the predetermined bias voltage B, per minute in the 100- and 50-tons arc-fumace.

According to the system of the present invention, the charge melting process is divided into five stages as described above depending upon the arc-furnace conditions; the biases or predetermined values B to B are determined for thus divided stages respectively so as to be compared with the output signals from the respective comparators, thereby deriving the instructions for starting the respective divided operation stages, thus regulating the position and the lowermost position of the electrode. withinthe arc-furnace. Thus, the arc-furnace operating condition can be accurately detected without the visual inspection and optimal power supply can be done; the operation of arc-furnace comes to be uniform, regardless of quality and quantity of the scraps; the remarkable economy of the power consumption can be realized as compared with the conventional system; the service lives of the arc-fumace and the electric circuit can be increased; and the labor and the time required for operating the arc-furnace can be further reduced with improved results.

The present invention has been so far described with particular reference to one illustrative embodiment thereof, but it will be understood that variations and modifications can be effected by those skilled in the art without departing from the true spirit of the present invention as described hereinabove and as defined in the appended claims.

I claim:

l. A method for automatically detecting and controlling the furnace operating condition of an arc-furnace at the charge or burden melting stage characterized by deriving the signals representing the position and the lowermost position of an electrode, transmitting said signals to detecting means for detecting the first period, the boring down period and the establishing period of a small pool of liquid respectively, detecting the main melting stage by-means of the power consumed after the molten bath forming stage starting signal has been derived, and detecting the fiat bath period by detecting means which is energized by said signals representing the position and the lowermost position of said electrode and by the signal representing the arc impedance.

2. An automatic detecting and control system for detecting and controlling the furnace operating condition of an arc-furnace at the charge or burden melting stage characterized by the provision of means for generating the signals representing the position and the lowermost position of an electrode respectively, memory means for receiving said signal representing the lowermost position of said electrode from said signal generatin means and storing therein the magmtude of said signal w en the arc current starts to flow, a first comparator for comparing said signal representing the lowermost position of said electrode with a predetermined value, thereby deriving the boring down period starting signal, sampling means for storing per unit time said signals representing the lowennost positions of said electrode, a second comparator for comparing the signal from said sampling means with a predetermined value, a third comparator for comparing the signal representing the lowermost position of said electrode with a predetermined value, a first logic circuit for receiving the signal from said second comparator and the signal from said third comparator thereby deriving the establishing period of a small pool of liquid starting signal, a fourth comparator for receiving said signals representing the position and the lowermost position of said electrode, a fifth comparator for receiving the signal representing the arc impedance based upon the arc voltage and current and comparing it with a predetermined value, thereby deriving the pulses representing the number of times when said arc impedance signals exceed said predetermined value, a pulse counter for counting the pulses from said fifth comparator, a sixth comparator for' receiving the signal from said pulse counter and comparing it with a predetermined value, a second logic circuit for receiving the signals from said fourth and said sixth comparators, thereby deriving the flat bath period starting signal; and a seventh comparator for deriving the shielded arc period starting signal when the power consumed, after said establishing period of a small pool of liquid starting signal has been derived, coincides with a predetermined value. 

